There have so far been well-known processes for forming a color proof from a plurality of black-and-white half dot images prepared by a color-separation and a half dot image conversion in a color plate-making.printing process, such as an over-lay process in which a color image is formed by making use of a photopolymer or a diazo compound, and a surprint process.
The over-lay process has such an advantage that the operations are very simple and the production cost is inexpensive and, in addition, the process can also be utilized for proofing simply by superposing four color film sheets (in the primary colors of subtractive color mixture and black). However, this process has such a disadvantage that a gloss is produced by superposing the film sheets and, therefore, the resulting texture becomes different from the printed matter it represents.
The surprint process superposes colored images on a support. This type of process includes the well-known processes described in, for example, U.S. Pat. Nos. 3,582,327, 3,607,264 and 3,620,726, in which a colored image is obtained by utilizing the stickiness of photopolymeric materials and carrying out a toner development.
There are also the well-known processes as described in Japanese Patent Examined Publication No. 47-27441/1972 and Japanese Patent Publication Open to Public Inspection (hereinafter abbreviated to JP OPI Publication) No. 56-501217/1981, in which a color proof is prepared in the following manner. An image is formed by transferring it onto a support by making use of a light-sensitive colored sheet, by exposing it to light and then by developing it. After that, another colored sheet is laminated thereon and the same procedures are repeated so as to prepare the color proof.
There is also a well-known process as described in JP OPI Publication No. 59-97140/1084, in which colored images are obtained by making use of a light-sensitive colored sheet, the corresponding color-separation films are each exposed to light and developed, and the resulting colored images are each transferred onto a support so that a color proof can be formed thereon. The toners for forming the above-mentioned images and the colorants for colored sheets have the advantage that the same coloring materials used as printing inks can be employed Therefore, the resulting color proof closely resembles in color tone.
However, these processes have the following disadvantages. In the steps needed to prepare a color proof, images have to be superposed and transferred and it takes a long time to complete the operations and, in addition, the production cost is also expensive.
As for the processes capable of eliminating the above-mentioned disadvantages, there are the processes in which a color proof can be prepared by making use of a silver salt color photographic light sensitive material comprising a white support, such as disclosed in JP OPI Publication Nos. 56-13139/1981, 56-104335/1981, 62-280746/1987, 62-280747/1987, 62-280748/1987, 62-280749/1987, 62-280750/1987 and 62-80849/1987.
In these processes, a proofing image is used in the form of a color image that is formed in the following manner. Plural color-separated black-and-white halftone dot images are prepared by converting a colored original document into plural color-separated halftone dot images. The resulting plural B&W halftone dot images are printed one after another on one sheet of color paper in a contact printing method or the like. The printed images are color developed so that a color image formed of the dyes produced imagewise of the couplers. The resulting color image is to be used as the proofing image.
The above-mentioned technique, however, has the following defects. When a color image is approximated to a printed matter, the density of a black image such as the density of letters is inferior to that of the printed matter and, on the other hand, when the density is enhanced so that black image such as that of letters have the same density as the printed matter, the approximation degrees of the color image of the printed matter are deteriorated, so that neither density is satisfactory.
As for the techniques for improving the above-mentioned defects, there is a well-known technique in which the 4th black printer layer is arranged to have a spectral sensitivity different from those of any other layers, besides the yellow, magenta and cyan color developing layers. Japanese Patent Publication Open to Public Inspection (hereinafter abbreviated to JP OPI Publication) Nos. 2-289846/1990 and 2-183251/1990 each disclosed techniques for improving the above-mentioned problems. When the techniques are used, chromatic image densities may be lowered to some extent by separating each chromatic image density from a black image density, and to make each of the monochromatic hues approximate the same as those of a printed matter. However, the improvements thereof are still not satisfactory. In addition to the above, it was found out therefrom that the gradations of the color images formed from each photographic image also has an influence on the monochromatic tones. Therefore, studies were carried out to further improve the comprehensive color proof qualities such as the gradations, qualities and color hues of halftone dots.